Not Applicable.
Not Applicable.
This invention relates to wheel balancers and in particular to improved wheel balancers using rim runout and loaded wheel/tire assembly measurements.
The determination of unbalance in vehicle wheels is carried out by an analysis with reference to phase and amplitude of the mechanical vibrations caused by rotating unbalanced masses in the wheel. The mechanical vibrations are measured as motions, forces, or pressures by means of transducers, which convert the mechanical vibrations to electrical signals. Each signal is the combination of fundamental oscillations caused by imbalance and noise.
Even when a wheel/tire assembly is balanced, non-uniformity in the construction of the tire as well as runout in the rim can cause significant vibration forces as the wheel rolls under vehicle load. Most tire manufacturers inspect their tires on tire uniformity machines and grind rubber off the tires as required to improve rolling characteristics of the tires. Even after this procedure, tires will often produce vibration forces (not related to imbalance) of 20 pounds as they roll on a smooth road. To put this in perspective of balancing, a 0.8 ounce balance weight is required to produce a 20 pound vibration force on a typical wheel traveling at 70 mph.
Prior art balancers are also not well equipped to take into account and correct for variations in uniformity of the wheel rim and the tire. It would be desirable, for example, to place a measured amount of imbalance in a wheel to counter tire non-uniformity forces or to detect and mark the position on a tire which should be matched to a corresponding position on the rim to reduce vibration due to non-uniformity of either or both. To the extent that presently available balancers do measure rim and tire runout, it is believed that the information they acquire is not particularly useful to the operator. In particular, presently available balancers which do measure runout generally display that runout to the user in the form of sine waves referenced to some arbitrary point. For a conventional system, which typically measures radial runout of both rims, this results in two (basically incomprehensible) sine waves. Such a system could be improved.
Many conventional balancers also assume that the wheel/tire assembly which is suitably balanced under an essentially no-load condition will also be suitably balanced when installed on the vehicle and subjected to the substantial load represented by the weight of the vehicle. This assumption is not valid under all conditions. It would be preferable in many circumstances to simulate loaded conditions to improve the results of the balancing operation.
Among the various objects and features of the present invention is a wheel balancer with improved performance.
Another object is the provision of such a wheel balancer which is capable of simulating loads on the wheel/tire assembly.
Other objects and features will be in part apparent and in part pointed out hereinafter.
In one aspect of the present invention, a wheel balancer includes a shaft adapted for receiving a wheel/tire assembly, the shaft having a longitudinal axis and being rotatable about the axis so as to rotate a wheel/tire assembly removably mounted thereon, a rotation sensor assembly for measuring rotation of the shaft about its longitudinal axis, a vibration sensor assembly for measuring vibration of the wheel/tire assembly as the wheel/tire assembly is rotated, a motor operatively connected to the shaft for rotating the shaft about its longitudinal axis, thereby to rotate the wheel/tire assembly, a load roller for applying a generally radial force to the wheel/tire assembly during rotation of the wheel/tire assembly so that a loaded wheel/tire assembly measurement of the wheel/tire assembly while the force is applied thereto may be determined, a sensor for measuring the runout of the wheel rim of the wheel/tire assembly at the bead seat, a control circuit responsive to the measured vibration of the wheel/tire assembly to determine wheel imbalance, and responsive to the measurements of wheel rim runout and to the loaded wheel/tire assembly measurement to determine an angular remount position of the tire on the rim to minimize some predetermined uniformity parameter of the tire or wheel/tire assembly.